Thin film resistors are very attractive components for high precision analog and mixed signal applications. In addition to a low thermal coefficient of resistance and low voltage coefficient of resistance, thin film resistors provide good resistor matching and good stability under thermal stress. To achieve good stability under thermal stress, it is critical to not only control the resistance of the body of the thin film resistor, but also the resistance of the electrical interface layer to the thin film resistor. Ideally, the resistance of the electrical interface layer should not contribute to the resistance of the thin film resistor.
Typically, thin film resistor fabrication processes implement titanium tungsten (TiW) as an electrical interface layer to the thin film resistor layer. A disadvantage associated with using titanium tungsten (TiW) as the electrical interface layer to the thin film resistor layer is that titanium tungsten (TiW) contributes to the overall resistance associated with the thin film resistor layer. In other words, the resistivity of the thin film resistor is not well controlled by the titanium tungsten (TiW) electrical interface layer, and contributes to increased thermal stress and an increased thermal coefficient of resistance (TCR) of the thin film resistor. Another disadvantage associate with using titanium tungsten (TiW) as an electrical interface layer is high particulate levels, as well as maintenance issues associated with the high particulate levels.